Scientists and onlookers gathered Saturday at a Northern California beach to view a 79-foot-long blue whale — a member of the largest species on Earth — that washed up dead the day before after apparently being hit and killed in a collision with a ship.

The whale, an adult female, was found on Agate Beach in Bolinas along the Marin County Coast, about 10 miles north of San Francisco early Friday morning.

Scientists who on Saturday conducted an autopsy, known as a necropsy, said it appears the animal was hit by a ship.

“We found out that it was blunt force trauma due to a boat strike,” said Barbie Halaska, a biologist and research assistant at the Marine Mammal Center in Sausalito. “The whole left side of her body was damaged. We found 10 broken ribs and 10 fractured vertebrae near the tail and mid-body.”

Halaska said that although large whales are sometimes towed out to sea when they wash up on beaches, this one will be left on the beach to decompose, be eaten by birds and wash back into the ocean. That’s because there is a large reef off the beach, which is adjacent to Point Reyes National Seashore, she said.

“There’s no way you could get a vessel in there to tow it out,” she said. “It would be very tricky.”

A 79-foot-long blue whale washed up dead Friday, possibly after being hit by a ship, at Agate Beach in Bolinas along the Marin County Coast. (Marine Mammal Center)

Ship strikes have been a recurring threat to whales around San Francisco Bay and other large ports.

Last October, a 65-foot-long blue whale washed up dead on Westmoor Beach in Daly City. That whale, a sub-adult male, was found to have died from a skull fracture as a result of a collision with a ship, scientists found.

Halaska said that some cargo ships are so massive that the operators don’t know when they have hit a whale, even one as big as a blue whale.

“It might slow down their speed one or two knots, but nothing they would notice,” she said. “These are huge boats. People who have come into port with whales on the bow of their ships have told us they had no idea.”

Less than a month ago, on May 1, the Greater Farallones and Cordell Bank national marine sanctuaries instituted a voluntary policy of asking the operators of large ships to slow their speeds roughly in half to 10 knots — about 11 mph — as they enter the shipping lanes heading toward the Golden Gate Bridge.

“Some ship strikes are inevitable, but we may be able to minimize the harm to whales if the ships are moving more slowly,” said Mary Jane Schramm, a spokeswoman for the Greater Farallones National Marine Sanctuary in San Francisco.

Blue whales are massive marine mammals. They can reach 100 feet in length and 300,000 to 400,000 pounds. Their tongues weigh as much an elephant and they can live 80 years or more.

The whales were decimated in the 1800s and 1900s by whaling, a practice that the United States outlawed in 1972. While other whale populations, including those of gray whales and humpbacks, have gradually recovered in numbers, blue whales remain listed as endangered under federal law and have been slower to come back.

Every spring, blue whales swim north from Costa Rica and Mexico up the California, Oregon and Washington coasts, following krill, the tiny shrimp-like animals that form the staple of their diets.

On Saturday, national marine sanctuary scientists cruised in boats off the San Francisco and Marin coasts, looking for “hot spots” of blue and humpback whales and radioing ships in the area to warn of their locations.

Often when whales die in ship strikes, they sink to the bottom of the ocean. Researchers at the Marine Mammal Center said this whale was found in relatively intact condition, which allowed them to take useful tissue samples to learn more about the animals.

Halaska said that scientists from the Marine Mammal Center, California Academy of Sciences and other organizations removed the stomach, liver, an eye, a part of the ear and other organs from the whale, which will help them learn whether it had any diseases, whether it had high levels of toxins, what it was eating and other facts such as its age.

“The opportunity to perform a necropsy on a carcass in this good of condition will help contribute to our baseline data on the species,” she said.

Saturday’s incident was only the ninth time in the 42-year history of the center that it has responded to a blue whale death.

Information from a photo database of blue whales based on their tail markings revealed a match with this weekend’s whale. It was first identified off California in 1999 and seen in at least 11 different years mostly in the Santa Barbara Channel area, according to the Marine Mammal Center.

There are between 8,000-9,000 blue whales worldwide. Roughly 2,800 blue whales feed along the California coast, according to the Marine Mammal Center. They make up the largest concentration of blue whales in the world.

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Paul Rogers has covered a wide range of issues for The Mercury News since 1989, including water, oceans, energy, logging, parks, endangered species, toxics and climate change. He also works as managing editor of the Science team at KQED, the PBS and NPR station in San Francisco, and has taught science writing at UC Berkeley and UC Santa Cruz.

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